Conventional disk drive systems may include a spindle motor, a recording medium mountable on the spindle motor, one or more heads, and a rotary actuator system. The storage medium encompasses rigid magnetic disks, flexible magnetic disks, magnetic tape, and magneto-optical disks. The magnetic tape and disks are often housed in a removable cartridge that is insertable into an aperture in the disk drive.
Because of the trend toward higher areal density of information on the storage media, flying height of the heads over the media often is minimized. Magneto-resistive ("MR") heads and giant magneto-resistive ("GMR") are often employed with media having relatively high areal density. Referring to FIG. 8A (Prior Art), an MR head is shown schematically. MR head 28' includes a magneto-resistive read sensor or read head 60 and a separate inductive write element or write head 62. Read head 60 includes an MR sensor 66, which is formed of magneto-resistive material, between shields 64a and 64b. FIG. 8B (Prior Art) illustrates terminals 80a and 80b, through which current I passes. FIG. 8C (Prior Art) illustrates a floating head 28' that includes terminals 80a and 80b, which are connected to a preamplifier 30', which is coupled to and a read channel 34'.
Referring to FIG. 9 to illustrate a conventional operation during which data is retrieved from a drive 14' by a computer, a signal 69' is sent from the computer to drive 14' though a standard computer SCSI interface 48b that connects to a SCSI interface 48a of drive 14'. Signal 69' is transmitted through drive 14', and head 28' moves in response to signal 69' to the appropriate track on disk 18. head 28' transmits a head signal 70' to a register 36', which typically is part of the integrated circuit that includes preamplifier 30'. Within preamplifier 30', head signal 70' is amplified and attenuated by a circuit 33' to an appropriate level to produce an amplifier output signal 71'. Recording channel 34' receives and conditions amplifier output signal 71' to produce a data output signal 72' that is communicated to the computer via the SCSI interfaces 48a and 48b.
A conventional recording channel 34' may include an automatic gain control module to adjust the signal gain, a low pass filter to limit high frequency noise, an equalizer for slimming signal pulses so that interference among adjacent pulses is reduced, a peak detection circuit that differentiates peaks by converting the peaks into zero crossings and utilizes a comparator gate to generate pulses out of the zero-crossing detection circuit, a phase lock oscillator that monitors the embedded clock and reconstructs time interval, and a data decoder that detects the presence or absence of zero crossings within each window and converts the data into its original form. Recording channel 34' may be formed on a single chip or a chip set of two or three chips. The chip(s) of recording channel 34' may be disposed on a main printed circuit board 50, which is typically disposed below the base plate of the drive 14', although other locations are possible.
Within a disk drive, an electrostatic charge may build up by ambient particles rubbing together or rubbing on the media and drive components, by the head rubbing on the disk, by insertion of a removable cartridge that may have a latent charge, and similar phenomena. Discharge of the electrostatic charge may cause damage to the drive and disk, especially drives that employ MR heads or GMR heads, although virtually any head of a disk drive or a tape drive may be damaged by a discharge of static electricity.
A typical MR head may tolerate approximately 50 volts, while a typical GMR head may tolerate approximately 15 volts. Voltage that exceeds these limits may damage the heads, especially the magneto-resistive element 66, even if applied for a only short period.
An electrostatic discharge ("ESD") event may damage a magneto-resistive head in two ways. First, a relatively small ESD event (or a series of small ESD events) may result in magnetic degradation of the magneto-resistive element, which may be exacerbated by changes in the physical or magnetic properties of the head shell or shields. Magnetic degradation changes the resistance of the MR head and GMR head, on which the operation of the head and the associated recording channel depend. Specifically, head signal 70' may be altered by magnetic degradation of element 66, which may produce errors in data output signal 72'. Second, a relatively large ESD event may result in physical damage to the GMR or MR head 28, (especially the magneto-resistive element 66), preamplifier 30', recording channel 34', the arm electronics module, disk surface 18, and other components.
An ESD event may affect the data recording process, produce chronic errors in data recording, and catastrophic damage to the media and drive components. It is a goal of the present invention to protect a disk drive (especially magneto-resistive heads) and media from damage and interference from ESD events.